1. Field of the Invention
The present invention relates to a heat generating apparatus, non-exclusively used as a heat source for a vehicle heating system, and operating on the principle that a viscous fluid subjected to a shearing action due to the rotation of a rotor element generates heat which is received by a heat exchanging liquid circulating through a heat receiving chamber and is carried to an objective heated area.
2. Description of the Related Art
Japanese Unexamined Patent Publication No. 8-337110 (the corresponding European Patent Publication is No. 0687584 A1 and the corresponding U.S. Patent Publication is U.S. Pat. No. 5,573,184) discloses a heat generating apparatus adapted for use in a heating system incorporated in an automotive vehicle. The heating apparatus includes a housing in which a heat generating chamber and a heat receiving chamber, or a water jacket arranged adjacent to the heat generating chamber, are defined. The housing rotatably supports a drive shaft via a bearing and a shaft sealing device. An outer end of the drive shaft and the housing support thereon a solenoid clutch which acts so as to connect the drive shaft to a vehicle engine via a belt-and-pulley mechanism, and to disconnect the drive shaft from the vehicle engine as required. The drive shaft has an inner end extending into the heat generating chamber and a rotor element is formed integrally therewith to be rotated with the drive shaft within the heat generating chamber. The heat generating chamber has an inner wall surface which cooperates with outer faces of the rotor element to define gaps therebetween in which a viscous fluid such as silicone oil is confined to generate heat. Namely, when the above-mentioned heating apparatus is incorporated in the vehicle heating system, the rotor element integral with the drive shaft is rotationally driven by the vehicle engine, and accordingly, the viscous fluid in the heat generating chamber is subjected to a shearing action by which the viscous fluid generates heat within the gaps between the inner wall surface of the heat generating chamber and the outer faces of the rotor element. The heat is transmitted to the engine cooling water flowing through the water jacket via the wall of the heat generating chamber, and therefore, the heat transmitted to the engine cooling water is carried to a heating circuit in which the heat is moved to the air with the vehicle compartment.
In the heat generating apparatus of JP-A-'110, the viscous fluid within the heat generating chamber is constantly being subjected to the shearing action to generate heat during the rotation of the rotor element and the drive shaft. Therefore, the viscous fluid within the gaps between the inner wall surface of the heat generating chamber and the outer faces of the rotor element constantly can hold heat to become excessively hot. As a result, the viscous fluid is apt to be thermally degraded, and also be physically degraded due to the cutting of the molecular chains in the viscous fluid which reduces the molecular weight thereof. Thus, the viscosity of the viscous fluid is decreased so as to cause a reduction in the heat generating performance of the viscous fluid, and the operating life of the viscous fluid is shortened. Replacement of the degraded viscous fluid having a reduced viscosity with a fresh viscous fluid requires removing the heat generating apparatus from the vehicle and disassembly of the apparatus per se. The removed and disassembly of the heat generating apparatus is very cumbersome and inconvenient.
Further, according to an experiment conducted by the present Applicant with respect to the heat generating apparatus, when the apparatus is driven under a specified severe operating condition, such as a high speed and lengthy operating condition, it was found that leakage of the viscous fluid from the apparatus occurs. The heat generating apparatus of JP-A-'110 aims to achieve a simpler construction thereof while the viscous fluid within the heat generating chamber is added at a filing rate of 100%. Therefore, a thermal expansion of the viscous fluid within the heat generating chamber due to heat generation is absorbed by an expandable elastic membrane which also functions as a shaft sealing element, and a compensating chamber arranged between the shaft sealing element and a bearing device for rotatably support the drive shaft. Thus, when the heat generating apparatus is operated at a nominal rotating speed of the drive shaft for a relatively short period of time, leakage of the viscous fluid does not occur. Nevertheless, when the apparatus is operated at a very high rotating speed of the drive shaft or when the apparatus is operated at the nominal operating speed of the drive shaft for a long period of time, the thermal expansion of the viscous fluid cannot be absorbed by the elastic deformation of the elastic membrane and a reduction in the volume of the compensating chamber to result in leakage of the viscous fluid. Since the leakage of the viscous fluid reduces the amount of viscous fluid held in the heat generating chamber, viscous fluid must be added to the heat generating chamber by disassembling the heat generating apparatus mounted in, e.g., an engine compartment of the vehicle. Further, the viscous fluid gradually leaking from the heat generating apparatus causes contamination in the engine compartment.
Furthermore, in the heat generating apparatus of JP-A-'110, the heat generating chamber is entirely filled with the viscous fluid, i.e., the filling rate of the viscous fluid for the heat generating chamber is approximately 100%. Therefore, an initial torque to start the rotation of the drive shaft and the rotor element is very large. Accordingly, at the starting of the vehicle engine, various problems, in which a cranking motor of the engine fails due to an excessive load applied to the motor and the solenoid clutch and the pulley-belt, slip occur. Also, the starting of the heat generating apparatus during the running of the vehicle provides a driver with an unpleasant feeling caused by the starting shock of the apparatus.
U.S. Pat. No. 4,974,778 and the corresponding German Patent Publication DE-3832966-A1 disclose a viscous fluid type heat generating apparatus provided with a housing in which a heat chamber and a fluid supply chamber communicating with the heat chamber via a fluid-supplying passage and a fluid-returning passage. The heating and fluid storage chambers are filled with a viscous fluid and a given amount of air. Thus, the viscous fluid can be supplied from the fluid supply chamber to the heating chamber, and also returned from the heat generating chamber to the fluid supply chamber. Accordingly, degradation of the viscous fluid can be prevented.
Further, in the heat generating apparatus of U.S. Pat. No. 4,974,778, an amount of the viscous fluid held in the apparatus can be reduced at the start of the operation thereof, and accordingly, a starting torque necessary for starting the heat generating apparatus can be reduced.
Nevertheless, according to an experiment on the heat generating apparatus of U.S. Pat. '778, conducted by the present Applicant, it was confirmed that when the apparatus is operated under a severe operating condition, i.e., under a high-speed continuous-running condition, the apparatus may allow leakage of the viscous fluid from the apparatus. Namely, in the heat generating apparatus, the fluid-supplying passage and the fluid-returning passage are separately formed in a partition wall between the heat generating chamber and the fluid supplying chamber. Thus, the heat generating chamber and the fluid supplying chamber communicate with one another only by the fluid-supplying and fluid-returning passages. The fluid supplying passage is usually closed by a closing element and the fluid returning passage is constantly kept open. Accordingly, the fluid returning passage works as a throttling orifice opening from the heat generating chamber toward the fluid supplying chamber. As a result, a pressure level in the heat generating chamber increases during a high-speed continuous-running condition and causes leakage of the viscous fluid from the heating chamber.
Japanese Unexamined Patent Publication (Kokai) No. 2-246823 and the corresponding U.S. Pat. No. 4,993,377 disclose a viscous fluid type heat generator for an automobile which is provided with a heat generating chamber in which a heat generating chamber is formed so as to fluidly communicate with a vacant space arranged adjacent to an innermost end of a drive shaft on which a rotor element is mounted so as to be rotated together with the drive shaft. The heat generating chamber and the vacant space may be filled with viscous fluid. If the vacant space is supplied with a given amount of air, a thermal expansion of the viscous fluid in the heat generating chamber can be absorbed by volumetric reduction in the air in the vacant space fluidly communicating with the heat generating chamber. Thus, the viscous fluid can be prevented from leaking from the heat generator.
Nevertheless, the heat generator of JP-A-'823 is provided with coaxially extending labyrinth recesses formed by cooperation between axial projections of an inner wall surface of the heat generating chamber and alternate axial projections of outer faces of the rotor element. The labyrinth recesses prevent the viscous fluid held in the heat generating chamber from circulating in the heat generating chamber. Accordingly, the physical and chemical properties of the viscous fluid must be degraded during the continuous use of the viscous fluid type heat generator.